Lady Masquerade Manga by Chiho Saitou

The distorted memory becomes a masquerade. Everyone hides behind a mask and performs the wildest acts with no consequence. But, life is not a masquerade. The main character is a girl who suffers daily from what she accidentally witnessed years ago.

She keeps having flashbacks of a gruesome scene. It always starts with her as a little girl following a black kitten, and suddenly the black kitten turns into a panther! A woman welcomes the panther to join her and the rest of the panthers. And then, unaware of the presence of the little girl, the group starts having "fun."

The girl becomes horrified by the scene. She makes a noise and they notice her.
"Hunt her down! Kill her!" the woman says to the panthers.

She managed to escape from the pack, but they got to her parents. In her flashbacks, her parents were chased and fell off a cliff. The authorities told her that it was a car accident. She has lived on the edge of illusion and reality until she sees the photo of the woman on a magazine.
A photo is all she needs to confirm what her flashbacks tell her. Now, she is ready to get even.